This application is based on French Patent Application No. 00 12 162 filed Sep. 25, 2000, the disclosure of which is hereby incorporated by reference thereto in its entirety, and the priority of which is hereby claimed under 35 U.S.C. xc2xa7119.
1. Field of the Invention
The invention relates to a domed divergent lens for microwaves and an antenna incorporating it, the antenna being mounted onboard a satellite for communicating with terrestrial areas over a wide field of view.
2. Description of the Prior Art
In a telecommunication system using non-geosynchronous satellites in low Earth orbit or medium Earth orbit, the Earth is divided into areas or cells each of which has a diameter of several hundred kilometers, and terminals in an area communicate via a base station in that area. In other words, to set up a call between two terminals in the same area, the first terminal sends a signal to the base station via a communication system onboard a non-geosynchronous satellite, and the base station then transmits the call to the second terminal, again via a satellite. For communication between two terminals in two different areas, a call is set up between the two base stations of the two areas, for example via a terrestrial network.
Because it is necessary to minimize the weight and bulk of equipment onboard a satellite, it is preferable for a send or receive antenna to be assigned to a plurality of areas. The antenna must therefore cover a very wide field of view. For example, for a satellite at an altitude of 1400 km, the field of view has an angle at the apex of 108xc2x0 for a telecommunications system whose coverage achieves an elevation of 10xc2x0.
Also, because the satellite is non-geosynchronous and the areas on the ground are fixed, the antenna must be a beam scanning antenna, i.e. the beam of the antenna must be in angular movement at all times. Finally, the difficulty of constructing this kind of antenna is increased by the fact that its gain must increase as a function of the pointing angle. As the pointing angle increases, the distance to the area increases, which causes attenuation due to the distance and to passing through the atmosphere.
To satisfy the above requirements, there has already been proposed an antenna including, on the one hand, an electronically scanned beam generator and, on the other hand, a dielectric domed divergent lens for increasing the field of view of the beam generator and correcting the gain as a function of the pointing angle. Splitting the beam generation function and the field of view increasing function with gain correction as a function of the pointing angle makes it possible to produce an antenna having an aperture angle from 60 to 120xc2x0. Also, the beam generator generally uses electronic scanning with a limited number of radiating elements. The dielectric domed divergent lens is made of a constant permittivity material onto which quarter-wave matching layers are molded.
However in practice a dielectric domed lens is incompatible with space applications because the dielectric materials are exposed to very high mechanical and thermal stresses during launch and in space. What is more, this kind of lens has a high mass, which is also difficult to reconcile with space applications.
The invention eliminates this drawback.
Thus the antenna according to the invention includes an electronically scanned array associated with a domed divergent lens to increase the field of view of the scanned array and the domed lens includes a plurality of metal waveguides with various lengths, the greatest length being that on the axis of the lens and the length decreasing toward the periphery.
Each waveguide constitutes a sensor/emitter and a phase-shifter, which provides the divergent lens function. As a waveguide is made up of simple metal walls, the antenna according to the invention is well suited to space applications.
The waveguides can have any section, such as a circular section, which is relatively easy to manufacture, a rectangular section or a hexagonal section, which has minimum losses.
In one embodiment the domed antenna is connected directly to a plane array of waveguides constituting the electronically scanned array. In this case, the number of waveguides in the array is the same as the number of waveguides in the lens and the waveguides of the plane array and of the domed lens are in one piece, for example.
The invention also relates to a domed divergent microwave lens including a plurality of waveguides with various lengths, the waveguides having a maximum length on the axis of the dome and the length decreasing as the distance from the axis decreases.
The invention therefore provides a domed divergent microwave lens including a plurality of waveguides with various lengths, the greatest length being that on the axis of the lens and the length being shorter for waveguides far from the axis.
In one embodiment the axes of the waveguides are all parallel to each other and parallel to the axis of the lens.
Alternatively, the axes of the waveguides converge at a point on the axis of the lens.
The lens is in the form of a body of revolution about an axis, for example.
All the metal waveguides preferably have the same section, for example a circular, rectangular or hexagonal section.
The invention also provides a send or receive antenna for a telecommunication system using non-geosynchronous satellites, the antenna being intended to form a set of fixed beams on the ground extending over a total angle of view from 60 to 120xc2x0, the antenna including an array of radiating elements scanned electronically to form beams corresponding to the various terrestrial areas and a domed divergent lens for enlarging the aperture of the beams created by the array of radiating elements and producing a gain that is at a minimum on the axis of the antenna and at a maximum at the periphery of the antenna, wherein the divergent lens includes a plurality of metal waveguides with various lengths, the greatest length being that on the axis of the lens and the length being shorter for waveguides far away from the axis.
In one embodiment the array of radiating elements includes the same number of waveguides as the domed divergent lens.
In one example, the radiating elements of the array of radiating elements each include a waveguide in one piece with a waveguide of the domed divergent lens.
In this case, in one embodiment, the waveguides of the array of radiating elements are extended by one or more sections for filter means on the side opposite the waveguides of the divergent lens.
Other features and advantages of the invention will become apparent from the following description of embodiments of the invention, which is given with reference to the accompanying drawings.